Fix defaults theme preview

Author: jhildenbiddle

docs/index.html

@@ -10,6 +10,7 @@
     <title>docsify-themeable - A delightfully simple theme system for docsify.js</title>
 
     <!-- Stylesheets -->
+    <link rel="stylesheet" data-style-group="themeable" href="https://cdn.jsdelivr.net/npm/docsify-themeable@0/dist/css/theme-defaults.css" disabled>
     <link rel="stylesheet" data-style-group="themeable" media="(prefers-color-scheme: dark)" href="https://cdn.jsdelivr.net/npm/docsify-themeable@0/dist/css/theme-simple-dark.css">
     <link rel="stylesheet" data-style-group="themeable" media="(prefers-color-scheme: light)" href="https://cdn.jsdelivr.net/npm/docsify-themeable@0/dist/css/theme-simple.css">
     <link rel="stylesheet" href="assets/css/main.css">